CN103018918A - Method and device for generating radial or angled polarization self-focusing Airy beam - Google Patents

Abstract

The invention relates to a method and a device for generating a radial or angled polarization self-focusing Airy beam. The method includes regulating polarization states of a collimating Gaussian beam to obtain a linear polarization Gaussian beam polarizing along a certain direction; performing light splitting to obtain a transmission beam, emitting the obtained transmission beam vertically to a spatial light modulator loaded with a phase information graph and then emitting the beam out in a reflecting manner after phase modulation; performing light splitting to obtain a reflected beam, subjecting the reflected beam to Fourier transformation and then converging the reflected beam by a convex lens so as to obtain a linear polarization self-focusing Airy beam through an annular stop at the focus point of the convex lens; and finally carrying out radial or angled polarization conversion to obtain the radial or angled polarization self-focusing Airy beam. By the method, self focusing can be carried out without any optical focusing elements, the light intensity in front of the focus point is low, the light intensity at the focus point is increased, energy is concentrated, and accurate positioning is achieved. The method can be applied to the fields of particle arrestance, biological medicines and the like, and belongs to the technical field of applied optics. In addition, the device is simple in structure and high in stability and is adjustable.

Description

A method and device for generating radially or angularly polarized self-focusing Airy beams

technical field

The invention relates to a method and a device for generating radially or angularly polarized self-focusing Airy beams. The generated beams can be used in the fields of particle capture, biomedicine, etc., and belong to the field of applied optics technology.

Background technique

Circularly symmetric Airy beams have aroused great interest and widespread attention due to their unique self-focusing properties, also known as self-focusing Airy beams. The so-called self-focusing refers to the focusing of the beam during the transmission process in free space or medium due to its own transmission properties without the aid of focusing optical elements. At the same time, the self-focusing phenomenon of the Airy beam is also very special. The light intensity of the beam is low before focusing, but the light intensity increases rapidly at the focus, and the energy is accelerated and concentrated. The maximum light intensity at the focus can reach the original Airy beam Dozens or even hundreds of times the maximum light intensity. The above-mentioned characteristics of the self-focusing Airy beam make it have great potential application value in the fields of biomedical treatment and optical micromanipulation. In recent years, self-focusing Airy beams have also been used for particle trapping and manipulation. Compared with the general optical tweezers device, due to the self-focusing characteristics of the Airy beam, the self-focusing Airy beam can obtain a smaller spot radius, a stronger light intensity distribution and a deeper depth of focus. The self-focusing Airy beam is a solid beam at the focal point. When it is specifically applied to the optical confinement of particles, it can only capture those particles whose refractive index is larger than the surrounding medium at the focal point, and is not suitable for capturing particles whose refractive index is smaller than the surrounding medium. . Therefore, transforming the solid beam at the focal point of the self-focusing Airy beam into a hollow beam with zero axial light intensity can greatly expand the application of the self-focusing Airy beam in many fields. For example, for particle trapping, it can not only break through the limitation of the above-mentioned refractive index conditions of the self-focusing Airy beam, but also weaken the scattering effect of light, minimize the optical heating damage to the trapped particles, and improve the optical trapping efficiency.

In recent years, vector beams with spatially varying polarization distributions have attracted widespread attention in academia due to their optical properties and great potential applications. Vector beams can be divided into uniformly polarized and non-uniformly polarized beams. Cylindrical vector beams are a typical type of cylindrical vector beams with spatially non-uniform polarization states. Cylindrical vector beams have important applications in particle trapping, optical data storage, heat treatment of materials, high-resolution imaging, electron acceleration, plasmon focusing, laser processing and free-space optical communication due to their characteristics under high numerical aperture focusing. has been extensively and in-depth researched. Radially polarized and angularly polarized beams are two special types of polarization in cylindrical vector beams. Radially polarized light has attracted much attention because of its polarization state symmetry about the optical axis and the fact that there is always zero light intensity on the axis. The local polarization state at any point (except the central point) on the beam cross section is linear Polarized, but the polarization direction is along the radial direction; the local polarization state of an angularly polarized beam at any point on its beam cross section is also linearly polarized, but the polarization direction is orthogonal to the radial direction. At present, there are many methods for generating cylindrical vector polarized beams in experiments, which can be classified into active and passive according to whether the generation method involves an amplification medium. Active generation methods involve the use of laser intracavity devices to oscillate the laser light in the cylindrical vector polarization mode, such as the use of intracavity axial birefringent components or axial intracavity dichroism created with tapered lenses and Brewster's angle reflectors There are also many passive generation methods, such as using optical fibers or using liquid crystal spatial light modulators or polarization converters in free space.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, and provide a method for generating radially and angularly polarized self-focusing Airy beams with important application value for technical fields such as particle capture and biomedical micro-nano surgery, and provide A device for generating self-focusing Airy beams with radial and angular polarizations is simple in structure, easy to adjust, and good in stability.

In order to achieve the above object, the technical solution adopted in the present invention is to provide a method for generating radially or angularly polarized self-focusing Airy beams, comprising the following steps:

(1) Adjust the polarization state of the collimated Gaussian beam to obtain a linearly polarized Gaussian beam polarized along a certain direction;

(2) After the linearly polarized Gaussian beam is subjected to spectroscopic processing, the obtained transmitted beam is vertically incident on the spatial light modulator loaded with the phase information map, and then emitted in a reflective manner after phase modulation;

(3) After spectroscopic processing, the obtained reflected beam is converged by a Fourier transform convex lens, and passes through the annular diaphragm at the focal point of the convex lens to obtain a linearly polarized self-focusing Airy beam;

(4) Perform radial or angular polarization conversion processing on the linearly polarized self-focusing Airy beam to obtain a radially or angularly polarized self-focusing Airy beam.

The technical solution of the present invention also provides a device for generating radially or angularly polarized self-focusing Airy beams. The laser emits a collimated Gaussian beam, and the polarization state of the beam is adjusted through a polarizer to obtain a linearly polarized Gaussian beam polarized in a certain direction. ; After the linearly polarized Gaussian light beam passes through the beam splitter, the obtained transmitted light beam is vertically incident on the spatial light modulator loaded with the phase information map, and the phase modulation is carried out on the liquid crystal display screen of the spatial light modulator, and then emitted in a reflective manner; Through the beam splitter, after the reflected light beam obtained is converged by the Fourier transform convex lens, the linearly polarized self-focusing Airy beam is obtained through the annular diaphragm; the annular diaphragm is arranged at the focal point of the convex lens; After placing a polarization converter, the polarization state of the polarization converter is adjusted to be radially or angularly polarized, and the linearly polarized self-focusing Airy beam passes through the polarization converter to obtain a radially or angularly polarized self-focusing Airy beam.

The laser is a semiconductor-pumped solid-state laser; the transmittance and reflectivity of the beam splitter are 50%; the spatial light modulator is a reflective spatial light modulator, and the phase information is input by a computer connected to it Figure: The light-transmitting part of the annular diaphragm is the ring-shaped area of the diaphragm, the circular region in the center of the diaphragm is the light-shielding part, and the inner and outer apertures of the diaphragm are fixed; the described polarization converter is a liquid crystal voltage-modulated polarization converter , through the computer to control the loading voltage and adjust the polarization state of the beam to achieve radial polarization or angular polarization.

Due to the application of the above-mentioned technical solution, the present invention has the following advantages compared with the prior art:

1. The Airy beam generation method provided by the technical solution of the present invention can perform self-focusing without the use of focusing optical elements, the light intensity before the focus is low, the light intensity at the focus increases rapidly, the energy is concentrated, and it can be precisely positioned and utilized.

2. The technical solution of the present invention directly uses linearly polarized Gaussian beams to generate radially or angularly polarized self-focusing Airy beams, and the method is simple and reliable.

3. The provided Airy beam generating device has a simple structure, is easy to adjust, and has good stability.

Description of drawings

Fig. 1 is a schematic structural diagram of a radial or angularly polarized self-focusing Airy beam generating device provided by an embodiment of the present invention;

Fig. 2 is a phase information diagram for phase modulation of a light beam provided by an embodiment of the present invention;

Fig. 3 is a schematic structural diagram of an annular diaphragm provided by an embodiment of the present invention;

Fig. 4 is the light intensity distribution diagram of the radially polarized self-focusing Airy beam generated in Embodiment 1 of the present invention (propagation distance z=0);

Fig. 5 is the light intensity distribution diagram of the radially polarized self-focusing Airy beam generated in Example 1 of the present invention (propagation distance z=0.25m);

Accompanying drawing 6 is the light intensity distribution diagram of the radially polarized self-focusing Airy beam generated in Embodiment 1 of the present invention at its self-focusing focus (propagation distance z=0.85m);

Fig. 7 is the light intensity distribution diagram of the radially polarized self-focusing Airy beam generated in Example 1 of the present invention (propagation distance z=1.50m);

Fig. 8 is the light intensity distribution diagram when verifying the radially polarized self-focusing Airy beam in Embodiment 1 of the present invention (the propagation distance z=0, the polarization direction of the polarizer is the vertical direction);

Fig. 9 is the light intensity distribution diagram when verifying the radially polarized self-focusing Airy beam in Embodiment 1 of the present invention (the propagation distance z=0, the polarization direction of the polarizer is the horizontal direction);

Fig. 10 is a diagram of the light intensity distribution when verifying the angularly polarized self-focusing Airy beam in Example 2 of the present invention (the propagation distance z=0, the polarization direction of the polarizer is the vertical direction);

Fig. 11 is a diagram of the light intensity distribution when verifying the angularly polarized self-focusing Airy beam in Example 2 of the present invention (the propagation distance z=0, the polarization direction of the polarizer is the horizontal direction);

In Fig. 1: 1, laser; 2, polarizer; 3, beam splitter; 4, spatial light modulator; 5, 9 and 11, computer; 6, convex lens; 7, annular diaphragm; 8, polarization converter; 10 , Beam analyzer.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example 1:

Referring to accompanying drawing 1, it is the structure diagram of a kind of radial and angular polarization self-focusing Airy beam generating device provided by the present embodiment, and this device comprises: laser 1, polarizer 2, beam splitter 3, spatial light modulator 4. Convex lens 6, annular diaphragm 7, polarization converter 8, beam analyzer 10, computers 5, 9 and 11.

A Gaussian beam is emitted by the laser 1. In the present embodiment, the laser 1 is a semiconductor pumped solid-state laser with adjustable power, the maximum power is 1.8W, and the wavelength is 532nm; the Gaussian beam is linearly polarized along the vertical direction through the polarizer 2. Gaussian beam; the linearly polarized Gaussian beam is divided into a reflected beam and a transmitted beam through the beam splitter 3, and the transmittance and reflection of the beam splitter 3 are both 50%, which can improve the energy utilization rate of the beam; the transmitted beam arrives at a vertical incidence Spatial light modulator 4, spatial light modulator 4 is a reflective spatial light modulator, its phase information is modulated by computer 5 through software loading phase information map, referring to accompanying drawing 2, it is used for adjusting light beam provided by this embodiment The phase information map for phase modulation. The linearly polarized Gaussian beam is phase-modulated on the liquid crystal display of the spatial light modulator and then emitted in a reflective manner; the phase-modulated beam is divided into a reflected beam and a transmitted beam by the beam splitter 3 again, and the reflected beam After being converged by the Fourier transform convex lens 6, pass through the annular diaphragm 7 at the focal point of the convex lens 6 to obtain a linearly polarized self-focusing Airy beam. Liye transformation and focusing; referring to accompanying drawing 3, it is the structural representation of the annular diaphragm provided by the present embodiment, the light-transmitting part of annular diaphragm 7 is ring-shaped, and the circular area of diaphragm center is the opaque blocking part, The radius of the inner ring is 1 mm, the radius of the outer ring is 2 mm, and the inner and outer apertures are fixed and non-adjustable; the linearly polarized self-focusing Airy beam passes through the polarization converter 8 to obtain a radially or angularly polarized self-focusing Airy beam. In this embodiment , the polarization converter 8 is a liquid crystal voltage-modulated polarization converter, and the applied voltage is controlled by a computer to adjust the polarization state of the light beam to realize radial polarization or angular polarization. To measure the radially and angularly polarized self-focusing Airy beams produced by the device provided in this embodiment, the beam profiler 10 can be connected to the computer 11, and the beam profiler 10 is used for observing and photographing the radially and angularly polarized self-focusing Airy beams. Light intensity distribution of a focused Airy beam at different propagation distances.

The method for generating radially and angularly polarized self-focusing Airy beams using the above-mentioned device provided in this embodiment, the specific operation steps are as follows:

1. A Gaussian beam is emitted from the laser 1. When the beam passes through the polarizer 2, the polarization angle of the polarizer 2 is adjusted so that the beam becomes a linearly polarized Gaussian beam polarized along a certain direction.

2. When the linearly polarized Gaussian beam passes through the beam splitter 3, it is reflected and transmitted, and the transmitted beam reaches the spatial light modulator 4 in the form of vertical incidence, and the phase information map is loaded to the liquid crystal display of the spatial light modulator 4 through the software program of the computer 5 On the screen, adjust the position of the liquid crystal display of the spatial light modulator 4, so that the transmitted light beam passing through the beam splitter 3 just irradiates the phase information map, and then emits in a reflection manner after phase modulation.

3. The liquid crystal display of the spatial light modulator 4 and the annular diaphragm 7 are respectively placed on the front focal plane and the back focal plane of the convex lens 6, and the convex lens 6 performs Fourier transformation and convergence on the beam obtained by phase modulation. The beam obtained through phase modulation is divided into two beams again by the beam splitter 3, and the reflected beam is Fourier-transformed by the convex lens 6 and then passes through the annular diaphragm 7 to obtain a linearly polarized self-focusing Airy beam. As shown in accompanying drawing 2, it is the phase information diagram used in this embodiment. By adjusting the parameters of the phase information diagram, the center spot radius of the generated light beam and the width and radius of the surrounding rings can be changed.

4. Place the polarization converter 8 close to the annular diaphragm 7, adjust the three-dimensional direction displacement and angle of the polarization converter 8, and change the loading voltage through the computer 9 software to realize fine adjustment. The mode of the polarization converter 8 is adjusted to radial polarization, and the linearly polarized self-focusing Airy beam passes through the polarization converter 8 to generate a radially polarized self-focusing Airy beam.

5. Place a beam analyzer 10 on the radial and angular polarization self-focusing Airy beam propagation paths, connect to the computer 11, change the distance from the beam analyzer 10 to the polarization converter 8, observe and photograph the radial polarization self-focusing Airy The light intensity distribution of the light beam at different propagation distances.

This embodiment takes the generation of radially polarized self-focusing Airy beams as an example, see Figures 4 to 7, they are radially polarized self-focusing Airy beams at propagation distances z of 0, 0.25m, 0.85m, and 1.50m respectively The light intensity distribution diagram at , where Figure 6 shows the focal length z=0.85m of the self-focusing Airy beam, where the light intensity distribution at the focus of the Airy beam is a hollow beam. The invention provides a self-focusing Airy beam with important application value for generating radially and angularly polarized self-focusing Airy beams for particle capture, biomedical micro-nano surgery and other technical fields.

The generated radially polarized Airy beam is verified by placing a polarizer between the polarization converter 8 and the beam analyzer 10, adjusting the polarization direction of the polarizer to the vertical direction, and at the propagation distance z=0 The light intensity distribution picture taken at the place is shown in Figure 8; the polarization direction of the polarizer is adjusted to the horizontal direction, and the light intensity distribution picture taken at the propagation distance z=0 is shown in Figure 9. It can be proved from the light intensity distribution diagrams of Fig. 8 and Fig. 9 that this embodiment generates radially polarized self-focusing Airy beams.

Example 2:

According to the technical scheme of embodiment 1, a kind of radial and angularly polarized self-focusing Airy beam generating device is constructed. In this embodiment, the generation of angularly polarized self-focusing Airy beam is taken as an example, and the generated angularly polarized Airy beam is authenticating. The generation method and verification method are the same as those in Embodiment 1, only the mode 8 of the polarization converter in step 4 is adjusted to angular polarization, and then the angularly polarized self-focusing Airy beam is generated. During verification, the polarization direction of the polarizer is adjusted to the vertical direction, and the light intensity distribution diagram taken at the propagation distance z=0 is shown in Figure 10; the polarization direction of the polarizer is adjusted to the horizontal direction, and at the propagation distance z = 0, the light intensity distribution map is shown in Figure 11. It can be proved from the light intensity distribution diagrams in Fig. 10 and Fig. 11 that the present embodiment generates angularly polarized self-focusing Airy beams.

Claims (7)

1. A method for producing radially or angularly polarized self-focusing Airy beams, characterized in that it comprises the steps: (1) Adjust the polarization state of the collimated Gaussian beam to obtain a linearly polarized Gaussian beam polarized along a certain direction; (2) After the linearly polarized Gaussian beam is subjected to spectroscopic processing, the obtained transmitted beam is vertically incident on the spatial light modulator loaded with the phase information map, and then emitted in a reflective manner after phase modulation; (3) After spectroscopic processing, the obtained reflected beam is converged by a Fourier transform convex lens, and passes through the annular diaphragm at the focal point of the convex lens to obtain a linearly polarized self-focusing Airy beam; (4) Perform radial or angular polarization conversion processing on the linearly polarized self-focusing Airy beam to obtain a radially or angularly polarized self-focusing Airy beam. 2. A device for generating radially or angularly polarized self-focusing Airy beams, characterized in that: the laser emits a collimated Gaussian beam, and the polarization state of the beam is adjusted through a polarizer to obtain a linearly polarized Gaussian beam polarized in a certain direction ; After the linearly polarized Gaussian light beam passes through the beam splitter, the obtained transmitted light beam is vertically incident on the spatial light modulator loaded with the phase information map, and the phase modulation is carried out on the liquid crystal display screen of the spatial light modulator, and then emitted in a reflective manner; Through the beam splitter, after the reflected light beam obtained is converged by the Fourier transform convex lens, the linearly polarized self-focusing Airy beam is obtained through the annular diaphragm; the annular diaphragm is arranged at the focal point of the convex lens; After placing a polarization converter, the polarization state of the polarization converter is adjusted to be radially or angularly polarized, and the linearly polarized self-focusing Airy beam passes through the polarization converter to obtain a radially or angularly polarized self-focusing Airy beam. 3. A device for generating radially or angularly polarized self-focusing Airy beams according to claim 2, wherein the laser is a semiconductor-pumped solid-state laser. 4. A device for generating radially or angularly polarized self-focusing Airy beams according to claim 2, wherein the transmittance and reflectance of the beam splitter are both 50%. 5. A device for generating radially or angularly polarized self-focusing Airy beams according to claim 2, characterized in that: said spatial light modulator is a reflective spatial light modulator, and a computer connected to it Input phase information map. 6. A device for generating radially or angularly polarized self-focusing Airy beams according to claim 2, characterized in that: the light-transmitting part of the annular diaphragm is the annular region of the diaphragm, and the center of the diaphragm is The circular area is the shading part, and the inner and outer apertures of the diaphragm are fixed. 7. A device for generating radially or angularly polarized self-focusing Airy beams according to claim 2, characterized in that: the polarization converter is a liquid crystal voltage modulation polarization converter, and the loading voltage is controlled by a computer , to adjust the beam polarization state to achieve radial polarization or angular polarization.

Images